As a check-out system for a mass retailer, there is a type in which a registration apparatus that generates accounting data required for payment of a transaction for each transaction, and a payment apparatus that processes the payment of the transaction based on the accounting data are separated. The registration apparatus waits for the input of data relating to merchandise sales. If the data relating to merchandise sales is input by an operator, the registration apparatus generates accounting data based on the data, and transmits the accounting data to the payment apparatus. The payment apparatus waits for the input of payment data for the accounting data. If the payment data is input by the operator, the payment apparatus processes the payment of a transaction based on the accounting data and the payment data. The check-out system of this type, in which the registration apparatus and the payment apparatus are separated, employs a dual system in which separate salespersons respectively operate the registration apparatus and the payment apparatus, or a sharing system, that is, a so-called semi-self-type in which a salesperson operates the registration apparatus and a shopper operates the payment apparatus.
In a case of the semi-self-type, if it takes time for the shopper to operate the payment apparatus, the subsequent shopper has to wait before executing their payment. In order to avoid such a delay, a plurality of payment apparatuses are connected to a single registration apparatus. The registration apparatus selects any payment apparatus at each transaction, and transmits accounting data to the payment apparatus. Therefore, the registration apparatus needs to select a payment apparatus which is a destination of accounting data for each transaction.